This invention relates to fuel controls and more particularly to a fuel control having means for providing, during starting, both fuel enrichment and hot start protection.
It is known that during the starting of a gas turbine engine, when fuel flow has been initiated, the engine is under-speed and under-temperature and it may be necessary, under some operating conditions, to provide extra fuel beyond what is normally required for satisfactory starting.
Typically, the control calls for a scheduled flow of fuel which, unless ignition takes place immediately, often results in an excess of the fuel in the combustion chamber such that when ignition does occur, there is created what is known as a "hot start", which may overheat and damage the turbine.
While previous fuel control systems are capable of providing increased fuel flow during starting, there is a pressing need for one which will not only augment normal fuel flow during under-speed conditions but will also automatically positively shut off all fuel flow to the engine during over-temperature or hot start conditions without, however, presenting a risk of inadvertent shut down once idle is attained.